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Electron paramagnetic resonance (EPR) investigations of the ordering behaviour in single crystals of Cr3+-doped dimethylammonium aluminium sulphate hexahydrate (DMAAS) are presented at the transition from the ferroelastic to the ferroelectric phase. The measurements on chromium-doped DMAAS show that the Cr3+ probe substitutes at aluminium sites. Remarkable line-shape changes and line splittings are observed in the EPR experiment in contrast to the findings of former 27Al nuclear magnetic resonance studies. The EPR measurements confirm the order-disorder character of the ferroelectric phase transition at 151 K on a microscopic level and give information about the local order parameter of the dimethylammonium reorientation and the relation of the dimethylammonium reorientational motion to the critical dynamics.

The EPR spectra of manganese in polycrystalline BaTiO3 and n‐BaTiO3 (lanthanum‐doped BaTiO3) are studied. The measurements are carried out in all four phases of BaTiO3 to follow the phase transformations of the ceramic material by means of the microscopic probe manganese. The valence state of manganese in BaTiO3 and n‐BaTiO3 is determined and the site of incorporation is estimated from the experimental spin‐Hamiltonian parameters obtained in this study on the basis of the existing results of single crystal EPR.

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The electron paramagnetic resonance (EPR) spectrum of Mnat ions in ferroelectric guanidiniuni aluminium sulfate hexahydrate is analyzed. It t.urned out that these impurity ions enter into regular -413+ lattice sites forming two non-equivalent magnetic hexaquo-manganese (11) complexes of axial symmetry. The hyperfine lines of several fine-structure transitions exhibit a hidden "spin-flip'' satellite structure. It results from the proton ligand hyperfine interaction in the magnetic hexaquocomplexes. A strong dependence on temperature and uniaxial stress is found for the zero-ficld splitting parameter D. I t s variation with temperature is discussed in terms of thermal latbice expansion and local lat,tice vibration effects. Gitteransdehnung und der Wirkung con lokalisierten Gitterschwingungen diskutiert. Das Elektronenspinresonanz (EPR)-Spektruni von